/**
 * Interface describing a standard Stack ADT.
 */
public interface Stack {
  
/** Add o to the top of this Stack.
 * Precondition: the stack is not full.
 * @param o The object to be pushed.
 */
 void push(Object o);
 
/** Remove and return the top element of this Stack.
 * Precondition: the stack is not empty.
 * @return the formerly top element of the stack.
 */
 Object pop();

 /** Return whether the stack is empty.
  * @return whether the stack is empty
  */
 boolean isEmpty();
 



}